Luteinizing hormone (LH) receptors on the corpus luteum and on Leydig cells in the testis bind luteinizing hormone (LH) and human chorionic gonadotropin (hCG) to regulate steroid synthesis and secretion from these glands. Our basic hypothesis is that hormone binding is accompanied by interactions of the LH receptor with other membrane components and with the cytoskeleton to produce hormone-receptor complexes capable of signal transduction. First, we will examine the interactions of the LH receptor with other plasma membrane proteins in cells capable of activating adenylate cyclase in response to hormone binding. We will compare the molecular dynamics of the LH receptors that bind hormone but are unable to transduce signal with those of functional LH receptor complexes. Second, we will examine specific membrane proteins that interact with the LH receptor following ligand binding, particularly those which might be present only when formation of the hormone-receptor complex leads to activation of adenylate cyclase. We will use biophysical methods including fluorescence energy transfer techniques to examine receptor- receptor interactions and photoactivated membrane probes to identify membrane proteins near the receptor. Third, we will determine how the cytoskeleton restricts the movement of LH, possible by confining receptor within sub-micron membrane domains. We will examine the lateral diffusion and trajectories of wild-type and mutant LH receptors in the presence and absence of an intact cytoskeleton using photobleaching recovery methods and single particle tracking techniques. Fourth, we will determine whether activation of phospholipase C is dependent on the organization and interactions of LH receptors present on the cell membrane. We will compare the molecular motions and interactions of sparsely expressed LH receptors in cells where phospholipase C is not activated with those of densely expressed LH receptors capable of activating both cAMP and phospholipase C. Colorado State University has an unusual confluence of expertise in reproductive physiology and instrumental facilities for membrane structural studies. This situation provides us a unique opportunity to study both LH receptor organization and how this organization modulates receptor function.